The Obama Administration has authorised the targeted killing of an American citizen in what is believed to be an unprecedented move in the War against Terror.

According to US media reports, the radical Muslim cleric Anwar al-Awlaki, who has been linked to last November’s attack on Fort Hood, Texas, and the failed Christmas day airline bomb plot, has been approved for capture or killing.

Mr Awlaki, who is in hiding in Yemen, is understood to have moved from encouraging attacks on the United States to participating in them directly, The New York Times reports.

He has been directly linked to Major Nidal Malik Hasan, the US army psychiatrist accused of killing 13 people at Fort Hood, Texas, and to Umar Farouk Abdulmatallab, the Nigerian who tried to blow up a Detroit bound plane with a bomb in his underwear on Christmas Day.

American counter-terrorism officials told the newspaper that Mr Awlaki was an operative of al-Qaeda in the Arabian Peninsula, the affiliate of the terror network in Yemen and Saudi Arabia. He is also believed to actively recruit new members for the terror network.

Experts said that targeting him was was extremely rare, if not unprecedented. A former senior legal official in the administration of George W. Bush told The New York Times he did not know of any American who was approved for targeted killing under the former president.

But the director of national intelligence, Dennis Blair, told a House of Representatives hearing in February that such a step was possible, without naming Mr Awlaki as a possible target. “We take direct actions against terrorists in the intelligence community,” he said. “If we think that direct action will involve killing an American, we get specific permission to do that.”

The possibility that Mr Awlaki might be added to the target list was reported by The Los Angeles Times in January, and Reuters reported on Tuesday that he was approved for capture or killing.

“The danger Awlaki poses to this country is no longer confined to words,” said an American official, who was not named. “He’s gotten involved in plots.”

The official added: “The United States works, exactly as the American people expect, to overcome threats to their security, and this individual — through his own actions — has become one. Awlaki knows what he’s done, and he knows he won’t be met with handshakes and flowers. None of this should surprise anyone.”

Mr Awlaki was born in New Mexico of Yemeni descent. He was interviewed by the FBI after the September 11, 2001, attacks when he was accused of serving as “spiritual adviser” to two of the attackers at his mosque in Falls Church. He was detained by Yemeni authorities in August 2006 and held for more than a year as part of a secret investigation

Describing Mr Hasan’s attack at Fort Hood on his website, which advocates violence against the West, he wrote: “Nidal Hassan [sic] is a hero. He is a man of conscience who could not bear the contradiction of being a Muslim and fighting against his own people. No scholar with a grain of Islamic knowledge can deny the clear cut proofs that Muslims today have the right — rather the duty — to fight against American tyranny.”

On Tuesday, Jane Harman, the chairwoman of a House subcommittee on homeland security described Mr Awlaki as: “probably the person, the terrorist, who would be terrorist Number One in terms of threat against us.”